mm: cleancache: fix corruption on missed inode invalidation

From: Pavel Tikhomirov <[email protected]>
Subject: mm: cleancache: fix corruption on missed inode invalidation

If all pages are deleted from the mapping by memory reclaim and also moved to the cleancache:

__delete_from_page_cache
(no shadow case)
unaccount_page_cache_page
cleancache_put_page
page_cache_delete
mapping->nrpages -= nr
(nrpages becomes 0)

We don't clean the cleancache for an inode after final file truncation (removal).

truncate_inode_pages_final
check (nrpages || nrexceptional) is false
no truncate_inode_pages
no cleancache_invalidate_inode(mapping)

These way when reading the new file created with same inode we may get these trash leftover pages from cleancache and see wrong data instead of the contents of the new file.

Fix it by always doing truncate_inode_pages which is already ready for nrpages == 0 && nrexceptional == 0 case and just invalidates inode.

---

 mm/truncate.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

@@ -517,9 +517,13 @@ void truncate_inode_pages_final(struct a
 		 */
 		xa_lock_irq(&mapping->i_pages);
 		xa_unlock_irq(&mapping->i_pages);
-
-		truncate_inode_pages(mapping, 0);
 	}
+
+	/*
+	 * Cleancache needs notification even if there are no pages or shadow
+	 * entries.
+	 */
+	truncate_inode_pages(mapping, 0);
 }
 EXPORT_SYMBOL(truncate_inode_pages_final);
 

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